Characterization and management of gastrointestinal (GI) adverse events (AEs) with zanidatamab + chemotherapy (CT) ± tislelizumab in first-line (1L) HER2-positive (HER2+) locally advanced or metastatic gastroesophageal adenocarcinoma (mGEA): Analysis from HERIZON-GEA-01.

Key Points

• To characterize gastrointestinal adverse events and their management in patients with HER2-positive locally advanced or metastatic gastroesophageal adenocarcinoma receiving zanidatamab and chemotherapy.
• Randomized 1:1:1 allocation of patients to treatment arms including zanidatamab with chemotherapy or trastuzumab with chemotherapy.
• Patients received diarrheal prophylaxis with loperamide for the first cycle when treated with zanidatamab.
• Treatment efficacy and safety were analyzed across different arms, focusing on adverse event profiles.
• Diarrhea was the most common adverse event, occurring in 83.0% of patients receiving zanidatamab + tislelizumab vs 79.0% for zanidatamab + CT and 53.3% for trastuzumab + CT.
• Median first-onset of diarrhea was within 3 weeks for most patients; 76% experienced it in cycle 1 with a duration of less than 2.5 weeks.
• Grade 1/2 diarrhea events were common, and the incidence of high-grade events was infrequent.